Autogenously-bonded needled nonwoven fabric and method of making same



Dec. 12, 1967 NEWMAN 3, 7,

AUTOGENOU DED NEEDLED NONWOVEN FABRIC AND METHOD OF MA G SAME Filed Oct. 5, 196

M 7 0 1 Z; flza dd (9 United States Patent 3,357,878 AUTGGENOUSLY-BONDED NEEDLED NON- WOVEN FAllRll C AND METHGD 6F MAK- ENG SAME Nicholas S. Newman, West The Kendall Company, of Massachusetts Filed Oct. 5, 1965, Ser. No. 493,044 Claims. (Cl. 161-450) Newton, Mass, assignor to Boston, Mass, a corporation ABSTRACT OF THE DISCLOSURE This invention relates to a method of improving the dimensional stability and decreasing the elongation of needled nonwoven fabrics, by bonding together at least some of the fibers constituting the fabric, particularly within the body of the fabric in its zone of greatest density. More particularly, the invention relates to a method for bonding at least some of the fibers lying within the interior of a needled nonwoven fabric, at the cross over points of these fibers, by means of an active or latent solvent for the fibers.

Needled nonwoven fabrics are an important article of commerce, widely used in the prepartion of blankets, interlinings, padding and insulating structures, rug underlays, and the like. They are produced from an unspun and unwoven batt or fleece of fibers by passing the fleece lmder a vertically reciprocating board which bears 'a multiplicity of barbed needles. These needles, penetrating through the fleece, engage a certain number of the generally horizontally oriented fibers and forcibly reorient them in a direction substantially normal to the general fiber orientation in a set of What has been termed ligations.

Such needled products owe their tensile strength and general structural characteristics to inter-fiber friction, the normal inter-fiber friction of the fleece being increased by the reorientation and compaction caused by the needling process. Although needling in the customary manner will impart sufficient tensile strength to a nonwoven fleece to allow its utilization for many purposes, conventional needled nonwoven fabrics are characterized by a rather high degree of easy elongation: that is, t y may be readily distorted, and lack dimensional stability. Attempts have been made to remedy this deficiency by several means. Repeated needlings may be resorted to: this, however, makes the nonwoven fabric more dense, boardy, and inflexible. The fleece may be saturated with a binder, such as a latex or polymeric dispersion, which is expensive and generally has an adverse effect on the loft and insulating value which it is desirable to maintain at a maximum. A quite common expedient is to needle the fibrous fleece into a base fabric such as gauze or scrim, for the sole purpose of making the nonwoven resistant to deformation under stress. Nonwovens needled into a base fabric do maintain their loft and insulating value, but the use of fabric bases is expensive.

I have found that if the ncedling operation is so conducted that an active or latent solvent for at least some of the fibers is applied to at least a part of the lower length of the needles during needling, the solvent is drawn up through the outer face of the fleece and is deposited in major portion throughout the interior of the fibrous mass, and particularly where the fiber-to-fiber contact points or crossing points are most numerous. As such crossing points, segments of fibers which contact each other aresoftened or swollen by the solvent action, and upon evaporation of the solvent they are bonded together by what may be termed an autogenous bond: that is, without the use of any foreign bonding material. In this manner, a high degree of dimensional stability may be imparted to the needled nonwoven fabric without excessive matting down of the natural fleecy surface and without the loss of loft and insulating value which accompanies such matting down. The process of this invention therefore is an improvement over the art of applying solvent-sensitive needled fibrous nonwoven fabrics by means of spraying, or by over-all saturation.

It is therefore an object of this invention to provide a process for imparting dimensional stability to needled nonwoven fabrics comprising solvent-sensitive fibers.

It is a further object of this invention to provide certain needled nonwoven fabrics in which the fibers in the interior of the fabric are autogenously bonded together.

Other objects of the invention will appear more fully from the following description and drawings, in which:

FIGURE 1 is a schematic representation, in cross-section, of an apparatus suitable for carrying out the process of this invention.

FIGURE 2 is a representation of a barbed needle, partially broken away, suitable for use in this invention.

FIGURE 3 is a cross-sectional representation of a product of this invention.

Referring to FIGURE 1, a fleece of textile-length fibers, as delivered from one or more cards, garnetts, air-lay machines or the like (not shown), is carried by a conveyor belt 12 to a needling device. The needling device consists essentially of a needle board 14 bearing a multiplicity of barbed needles 16 which, in an up and down movement, pass through perforated bed plates 18 and 20, said bed plates confining the fleece during the needling operation.

Mounted below the lower bed plate 20 is an open container of solvent 24, said container being conveniently in the form of a shallow tray 22. The level of the solvent may be regulated by a conventional ball and cock valve arrangement or by an overflow or other constant level device, not shown. During the downward thrust of the needles 16 through the 'bedplates 18 and 20, the needles dip below the surface of the solvent 24, to an extent determined by the amount of solvent it is desired to apply to the fleece. As the needle board and its needles are retracted upwardly to complete the strike, the solvent which has been deposited on the needle shanks is to a large extent wiped off by and deposited onto the fibrous fleece, said deposition being most extensive in the interior of the fleece where the fiber density is highest, as explained more fully hereinbelow.

From the combined needling and solvent application operation the condensed web is conveniently drawn by a pair of draw rolls 34, 36, under one or more infrared dryers 28, 30, 32, passing in dried condition from the draw rolls to a Windup device, not shown. Instead of infrared dryers, steam-heated cans, tunnel dryers, or other alternatives may be used.

FIGURE 2 represents a partially broken away view of a single needle, 40, showing the cavities which accompany the barbs 42 as filled with solvent 44, derived from the immersion step outlined under the discussion of FIGURE 1. This is an idealized situation, since in most cases there is at least a partial film of solvent over the surface of the needle shank, as well as random solvent droplets thereon. Nevertheless, it is felt that the barbs do contribute substantially to the pick-up and transfer of the solvent.

FIGURE 3 represents a cross-sectional view of a typical product of this invention, only a few fibers being shown to allow for clarity of detail. This figure may be regarded as a cross-section through a single needle punching or ligation, formed by a single needle traversing through the fleece from above, downward, dipping into the solvent during a part of its lowermost stroke cycle, and then being retracted upwardly to deposit most of its burden of solvent within the interior of the fleece, and particularly in the vicinity of the ligation.

In a fibrous fleece as delivered by a card, garnett, or cross-lay machine, the fibers are generally oriented in what may be considered a horizontal direction, although a certain number of fibers may make a substantial angle withthe horizontal and run from one surface of the fleece to another along at least a part of their lengths.

Within this horizontal Stratification the fibers may be rather highly parallelized, as from a card, or at random angles to each other, as from an air-lay machine. The general effect of a needle thrust is to forcibly reorient some of the horizontal fibers into a vertical position for at least a part of their length, and to accentuate the vertical disposition of those fibers which were disposed more or less vertically to begin with. Microscopic examination of the ligations formed in needled fleeces reveals the presence of fibers 50 which are predominantly vertical, other fibers 51 which have both vertical and horizontal components, and fibers 53 which are predominantly horizontal.

Due to the compacting effect of the needling operation, which is most effective at and immediately around the vicinity of the actual ligation, the fibers in that region (as represented by the dotted circle in FIGURE 3) are brought into closer proximity than they are throughout the unperturbed area of the fleece. The solvent adherent to the needle shank is therefore wiped off the shank at the point of highest fiber density, which in turn means the point where the inter-fiber capillary attraction is greatest. The solvent therefore tends to remain in the immediate vicinity of the ligations, fortifying the internal structure of the needled fleece. Since the fiber density is low on the fuzzy fleece surface, little or no solvent is deposited there initially during the needles traverse. With both of the above factors operating to encourage solvent deposition and retention within the fleece interior, the loft, softness and insulating valve of the surface layers are virtually unaffected, a result unattainable by prior-art methods involvin g solvent spray or solvent immersion.

Referring still to FIGURE 3, the dark areas 52 represent portions of dissolved or swollen fiber substance caused by solvent deposition and subsequent solvent evaporation to leave solid fiber substance forming a series of autogenous fiber-to-fiber bonds within the interior of the needled fibrous fleece.

The invention will be illustrated by means of the following example.

Example I A crosslaid fleece of polyacrylonitrile fibers of 2 inch staple length, weighing 180 grams per square yard, was prepared from a blend of 50% 3 denier, 40% 5 denier, and 8 denier fibers. The fleece was needled six times in a Hunter fiber-locker with barbed needles in a scattered pattern, 48 needles per square inch at A inch advance.

The needled nonwoven fabric thus produced had a tensile strength of 11 pounds per inch-wide strip in the machine direction and 14 pounds in the cross direction. It was, however, dimensionally unstable and distorted readily upon being pulled by hand. The elongation at break was 102% in the machine direction and 106% in the cross direction.

The experiment was then repeated exactly except that the needles at the end of their downward traverse dipped into a tray containing 5% of ethylene carbonate, 5% of a silicone softening agent, and water. A total of wet pickup was noted, or 7% net addition of ethylene carbonate. After drying, the tensile strengths were substantially the same as the control sample, but the elongation was reduced to 31% in the machine direction and 40% in the cross direction. In addition to the marked decrease in elongation at break, the easy elongation was markedly diflerent between the control and the treated sample. The former distorted readily under the modest stresses involved in winding and unwinding from rolls, laying-out for cutting, etc. The treated sample not only was capable of being thus handled without distortion, but had suflicient stability to withstand dyeing, shearing, brushing, etc.

The solvent of choice for the practice of this invention will depend on the nature of the fibers being needled to form the nonwoven fabric. Ethylene carbonate and dimethyl sulfoxide are suitable for acrylic fibers: acetone, methyl ethyl ketone and other ketones for acetate fibers; dimethylformamide for polyester fibers, and phenol for polyamide fibers. Other solvents and solvent mixtures will suggest themselves to those skilled in the art. Blends of fibers may dictate a mixture of solvents each of which has its effect only on one fiber species. If desired, softening agents, antistatic agents, water-repellants, flameretardant agents and other textile auxiliaries commonly used in textile finishing may be dissolved or dispersed in the primary solvent bath.

The solvent used may be one which swells, gelatinize or dissolves the fiber substance readily at room temperature, or it may be a latent solvent which affects the fibers only at elevated temperatures, in which case the actual fiber-to-fiber bonding in the interior of the nonwoven fabric takes place in the drying or heating stage.

In the case of cellulosic fibers as cotton or rayon, the solvents which cause swelling or dissolution of the fibrous substance are liable to be strongly alkaline or acid, with corrosive action on the needles and on other parts of the equipment. They are also in general nonvolatile, and their residual traces after drying must be removed by a washing operation. In the case where cellulosic fibers are blended with solvent-sensitive synthetic fibers, therefore, it is within the scope of this invention to add to the solvent for the synthetic fibers a small amount of a substance serving as a binding agent for the cellulosic fibers, such as a solution or dispersion of a polymeric binder. The amount of such a binder, however, preferably does not exceed one-half of the net amount of solvent added to the needled fleece, since the primary desired effect is the ,autogenous bonding of one synthetic fiber to another at their crossover points in the region of greatest fiber density.

In addition to imparting a high degree of dimensional stability to needled nonwoven fabrics, allowing any supporting scrim or base cloth to be dispensed with, the process of this invention improves the degree to which the protruding surface fibers, constituting the nap or fleecy surface of the fabric, are anchored into the body of the fabric. By providing a multiplicity of points at which the fibers are bonded to each other at the points of greatest fiber density, the process of this invention simultaneously increase the resistance of the outwardlyextending segments of the fibers to being plucked, rubbed, or scuffled off when subjected to frictional contact in use.

Having thus described my invention, I claim:

1. The method of producing an autogenously-bonded needled nonwoven fabric which comprises preparing a fleece-like array of unspun and unwoven textile-length fibers oriented predominately in the principal plane of the array,

thrusting through said fibrous array a multiplicity of barbed needles,

engaging at least a portion of the fibers in said array with the barbs of said needles,

forcibly displacing the engaged portion of said fibers into a direction generally normal to the plane of said array,

prolonging the traverse of said multiplicity of barbed needles beyond the lower boundary plane of said fibrous array,

applying to at least a portion of the length of said needles a solution comprising a substance which is a solvent for at least one class of the fibers in said array,

retracting said multiplicity of barbed needles upwardly through said fibrous array,

and depositing the material applied to said needles on and within the fibrous array,

said deposition occurring principally in the regions of highest fiber density and closest fiber-to-fiber approximation.

2. The process according to claim 1 in which the fibrous array is composed at least in part of polyacrylic fibers and the solvent is ethylene carbonate.

3. The process according to claim 1 in which the 4. An autogenously-bonded needled nonwoven fabric which comprises an unspun and unwoven needled array of textile-length fibers,

said fibers being bonded together at .at least some of their crossover points,

said bonding being derived from the adhesion of fiber to fiber by means of fiber substance,

said bonding occurring principally in the internal region of said fabric,

the fibers at and near the surfaces of said fabric being substantially unbonded.

5. The product according to claim 4 wherein at least a portion of the fibers are polyacrylic fibers.

References Cited UNITED STATES PATENTS EARL M. BERGERT, Primary Examiner. HAROLD ANSHER, Examiner. 

4. AN AUTOGENOUSLY-BONDED NEEDLE NONWOVEN FABRIC WHICH COMPRISES AN UNSPUN AND UNWOVEN NEEDLED ARRAY OF TEXTILE-LENGTH FIBERS, SAID FIVERS BEING BONDED TOGETHER AT AT LEAST SOME OF THEIR CROSSOVER POINTS, SAID BONDING BEING DERIVED FROM THE ADHESION OF FIBER TO FIBER BY MEANS OF FIBER SUBSTANCE, SAID BONDING OCCURRING PRINCIPALLY IN THE INTERNAL REGION OF SAID FABRIC, THE FIBERS AT AND NEAR THE SURFACES OF SAID FABRIC BEING SUBSTNTIALLY UNBONDED. 